How to Crack the Tire Code
Have you ever bought tires or stared at your own tires and wondered what the heck all the numbers and letters mean? You probably aren’t the only one. Here’s a handy guide to know what all those tire codes mean.
Tire Service Ratings
The first thing you will notice on the tire number is likely either a letter or a group of letters. Here are the most common distinctions.
P=passenger vehicle – This is the most common tire letter you will see and designates the tire for use on cars, minivans, light-duty trucks and SUVs.
LT=light truck – These tires are designed for vehicles used to tow trailers or heavier-duty applications like ¾ and 1-ton HD trucks and full-size vans.
LT (suffix)=light truck – If you have an LT suffix like “9.5-16.5 LT” on your tire, this means the tire is made for light-duty, medium-duty and heavy-duty trucks, some SUVs and vans. These tires are broken down into three categories: numeric to carry heavy loads, wide base for larger wheel rims and flotation for loads on loose surfaces.
T=temporary spare – This is a pretty straightforward tire designation and it only applies to spare tires.
ST=special trailer – The ST designation is commonly found on special trailer tires like those used boats and utility trailers.
C=commercial – The C is for commercial applications like delivery trucks and vans. When the C is used, it is commonly paired with a load range letter as well (like B, C or D).
Tire Sizes Decoded
Along with the type of tire, the tire code also gives the tire width, aspect ratio of the sidewall and tire/wheel diameter.
Tire Width – Normally, the tire width is found right after the letter designation and is commonly displayed in millimeters. For example, a P225 is a passenger tire that is 225 millimeters wide.
Sidewall Aspect Ratio – After the type and width, there is another number usually separated by a “/”. This number is the sidewall distance. It is basically the ratio of the height to width of the tire.
In a nutshell, all you need to know is the lower the number, the shorter the sidewall and vice versa. For example, low-profile tires have much lower aspect ratios while larger off-road tires with lots of tread have a higher aspect ratio.
Normally, any tire with an aspect ratio of 50 or less is considered a low-profile tire.
Tire/Wheel Diameter – This number is preceded by an “R” and indicates the tire and wheel diameter. This is number is usually expressed in the following: 8, 10, 12, 13, 14, 15, 17, 18, 19, 20, 22, 23, 24, 26, and 28.
All this number means is the rim width to fit the tire width. For example, R17 tires need to matched with 17 inch rims.
Here’s a handy video that helps break down the information above in an easy to understand format:
Additional Tire Codes
Along with the basics, there are a variety of other tire codes you may want to be aware of.
Construction Type – As we said above, the “R” code talks about the tire/wheel diameter. However, it also designates how the tire was made. There are three different distinctions for tires:
- R – radial tire construction
- D – bias-ply tires
- B – belted
While radial is the most popular, you will see bias ply used in some off-road vehicles. Belted tires are rarely seen these days.
Speed rating/Service Description – Believe it or not, tires have a speed rating. Why? Sports cars mainly.
The speed rating is the same letter as the service description. This letter designates both the speed and tire’s load index. For sports cars, there is a special “Z” rating distinction.
Treadwear/Traction/Temperature – Along the top, you may see treadwear/traction/temperature information. Here is how they break down:
- Treadwear – a relative figure based on a test vehicle’s 7,200-mile test compared with reference tire. This number is generally shown in hundreds. For example, a “200” means it will last twice as long as the test and “300” will last three times.
- Traction – This is a designated by a letter like AA, A, B or C and references how well the tire did on a straight-line test. The test drags the tire on a straight-line at 40 mph across a wet surface with it locked up (not allowed to rotate).
- Temperature – This letter indicates how well the tire handles the heat. Simply put, when you drive faster, heat increases and this letter says how much heat the tire can withstand. Like the traction letter, it is rather imprecise. For reference: “A” = 115 mph, “B” = 100-115 mph, “C” = 85-100 mph
Certain tires come with icons and letters indicating their purposes after the generic information. These distinctions can include many things like:
- M+S – mud and snow tire
- Mountain Snowflake Icon – meets minimum performance requirement for snow
- Original Equipment Marking – symbol or letters designating the tire is the automaker specified version for the vehicle.
- For the Toyota Tundra tire, you may have seen a 114 T DT on the tire. The 114 is the speed rating. The “T” is the letter noting the tire is Toyota approved for the vehicle and the “DT” designated the tread is Toyota approved.
- Red dot is a radial force high point mark
Lastly, every tire made in the U.S. must have a U.S. Department of Transportation label. This code is broken down into the following:
- First two letters indicate the factory
- Next five or six are manufacture specific jargon for tracking purposes
- Last four are date of production (first two for which of the 52 weeks, the second two for the year)
- If the string of numbers ends in a “-S” it simply means the tire complies with European noise regulations
One thing is for sure on tires. There certainly is a lot of information on them!
Filed Under: Maintenance Tips